Most dryers have a 5000 watt 240 volt heating element, a 120 volt motor, and 120 volt controls. They usually have a 3 position terminal block in the back.
If you're going to re-connect the dryer for 120 volts, be aware of a few things.
1) If there's a warranty, you'll void it.
2) You'll also violate the UL listing.
3) Most dryers have a 5000 watt 240 volt heating element. If this element is operated on 120 volts, it'll draw 10.4 amps, and produce 1250 watts. This means that it'll take basically 4 times as long to dry a load of clothes.
4) The motor and controls are already 120 volts, this change will have no effect on them.
The procedure is very simple; One of the outside poles of the terminal block will have two wires on it, the other will have one. The black wire of the cord goes to the terminal that has two wires on it. Use a #12/3 cord. The white wire of the cord goes on the center terminal. Install a jumper from the center terminal to the outside terminal that has one wire on it. If there's a jumper from the center terminal to the frame, remove it. The green wire of the cord goes on the ground (usually green) screw on the frame.
There, now you have a 120 volt dryer that'll take a much longer time to dry a load of clothes. No need to worry about fire here, the element will never get hot enough to ignite anything.
Rob